How long should I workout? I get that question a lot. First, lets separate three activities: weight lifting, cardio and abs.
Lets start with the weight lifting, everybody is different but work out too long and you waste your time. Who wants to waste time, correct? Workout smart! When you are doing intense workouts with heavy weights, you deplete your mental and physical reserves of energy and working out more than 60 minutes can be counter productive. (If you are really hardcore and want to workout two hours a day even though you are doing intense workouts you can do a split workout where you do one body part in the early morning and an un-related body part in the evening.) I suggest before you step foot into the gym you decide how long you will be there. Aim for an intense 45 minutes. No more! Once in the weight room you need to stay focused, look at the clock when you start your first rep and make a mental note of when you need to leave. Wear your ipod, keep your head down and stay focused and you can get a great workout in a short amount of time.
Cardio time is separate and how long you should do cardio depends on if you are trying to lose weight or are doing it for just general cardiovascular health. If you just want to keep healthy then 30 minutes of walking per day is fine but if you want to lose weight you are going to need to try and do 60 minutes per day of a strenuous exercise like swimming, biking or running. Another question I get all the time is “Do you do the cardio before or after weight lifting?” Honestly, it would be best if it was at some other time in the day but that is not practical for most people. I don’t even have time for that on most days. Most of us don’t like doing stationary cardio in the gym so do it before or after your weight lifting, whichever you find easier because its better to do it at the “wrong time” than not at all. If you are really concerned, do it AFTER your weight training.
Abs are a separate workout and I usually do them with my cardio or before starting my weight workout. The main point is not to interfere with your main weight workout by trying to do ab exercises between sets. The most effective ab exercise is the forearm plank. Start with 20 secs and build from there. Your goal is 2 minutes.